Refrigeration Cycle

ABSTRACT

Provided is a refrigeration cycle wherein, when an orifice is disposed within a refrigeration circuit, and a differential pressure between the upstream side and the downstream side of the orifice is detected using two pressure sensors, the difference between the characteristics of the pressure sensors can be adequately and easily absorbed in software, to accurately determine an actual differential pressure, so that the flow rate of refrigerant and the torque of a compressor can be accurately estimated. The refrigeration cycle wherein the orifice is provided within a refrigerant circuit, and the pressure sensors are respectively provided on the upstream side and the downstream side of the orifice, is characterized in that, with regard to output characteristics representing the relationship between the detected pressure and the sensor output of each pressure sensor, the difference between the output characteristics of one pressure sensor and the output characteristics of the other pressure sensor is determined based on the outputs of both pressure sensors at a condition where the flow of refrigerant is stopped.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a refrigeration cycle, andspecifically, to a refrigeration cycle which has an orifice and twopressure sensors disposed on the upstream and downstream sides thereof,which enables to estimate a flow rate of refrigerant, a compressortorque, etc. more accurately and which is suitable in use for an airconditioning system for vehicles, etc.

BACKGROUND ART OF THE INVENTION

For example, in a refrigeration cycle having a compressor, a condenser,a pressure reduction/expansion mechanism and an evaporator in thisorder, for example, in a refrigeration cycle of an air conditioningsystem for vehicles, there is a case where pressure sensors arerespectively provided at an upstream position and a downstream positionin the flow direction of refrigerant in a refrigerant circuit, and adifferential pressure between the pressures detected by both pressuresensors is determined. Further, in order to give a clear differentialpressure efficiently within a short zone, usually, it is effective toprovide an orifice (for example, Patent document 1). If thisdifferential pressure can be accurately determined, it becomes possibleto accurately estimate a flow rate of refrigerant having a highcorrelation with the differential pressure, and further, to accuratelyestimate a torque for driving a compressor using the flow rate ofrefrigerant. If the compressor torque can be estimated accurately and atreal time, it also becomes possible to reflect it to a control of avehicle engine as a drive source for the compressor, etc. (for example,engine fuel injection control), and it may contribute to save the fuelconsumption of the vehicle.

As described above, although it becomes possible to estimate a flow rateof refrigerant at that time based on a predetermined relationshipbetween a differential pressure and a flow rate of refrigerant byproviding pressure sensors respectively on the upstream and downstreamsides of the orifice in the refrigerant flow direction and determiningthe differential pressure between the pressures detected by bothpressure sensors, in order to carry out this estimation at a highaccuracy, it is necessary to determine the differential pressure at ahigh accuracy. Then, in order to determine the differential pressureaccurately, it is necessary at least that the pressure detectionproperties of both pressure sensors are same, or that the pressuredetection properties are recognized clearly. Each pressure sensor itselfdoes not have so great problem as long as a single pressure sensordetects a pressure at a certain position, because it has an excellentrepeatability with regard to the relationship between the detectedpressure and the sensor output. However, in case where a plurality ofpressure sensors are provided, there is a case where a slight differenceoccurs between the respective pressure sensors with regard to the outputcharacteristics representing a relationship between a detected pressureand a sensor output ascribed to an error of manufacture of pressuresensors, etc. Since the above-described differential pressure betweenthe upstream and downstream sides of the orifice may become a muchsmaller value as compared with the absolute value of the pressuredetected by each pressure sensor, if there is a slight difference inoutput characteristics between the respective sensors, there is a highfear that the difference appears as a relatively large error relativelyto the accuracy of the differential pressure to be determined. If arelatively large error occurs in the determined differential pressure,high-accuracy estimation of flow rate of refrigerant or torque ofcompressor cannot be expected.

PRIOR ART DOCUMENTS Patent Documents

Patent document 1: JP-A-6-281300

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Accordingly, an object of the present invention is to provide arefrigeration cycle wherein, when an orifice is disposed within arefrigeration circuit and a differential pressure on the upstream anddownstream sides thereof is detected using two pressure sensors, thedifference between the characteristics of the respective pressuresensors can be adequately and easily absorbed in software, to accuratelydetermine an actual differential pressure, so that the flow rate ofrefrigerant and the torque of a compressor can be accurately estimated.

Means for Solving the Problems

To achieve the above-described object, a refrigeration cycle accordingto the present invention wherein an orifice is provided within arefrigerant circuit, and pressure sensors are respectively provided onan upstream side and a downstream side of the orifice, is characterizedin that, with regard to output characteristics representing arelationship between a detected pressure and a sensor output of each ofthe pressure sensors, a difference in characteristics between outputcharacteristics of one pressure sensor and output characteristics of theother pressure sensor is determined based on outputs of both pressuresensors at a condition where a flow of refrigerant is stopped.

In such a refrigeration cycle according to the present invention, sincea difference in output characteristics between output characteristics ofthe respective pressure sensors disposed on upstream and downstreamsides of the orifice is determined at a condition where a flow ofrefrigerant is stopped, which is considered to be a condition at thatboth pressure sensors substantially detect a same pressure, it becomespossible to accurately determine the difference in outputcharacteristics between the respective pressure sensors ascribed toerror in manufacture, etc. of the respective pressure sensors, itbecomes possible to accurately recognize the difference in outputcharacteristics in advance before an actual detection or control iscarried out, and as needed, it becomes possible to carry out acalibration in software between the pressure sensors. Since such acalibration in software can be accurately carried out without adding amechanical processing to a pressure sensor itself, it can be performedvery easily. Then, if the calibration between the pressure sensors canbe carried out accurately, an actual differential pressure can bedetermined accurately.

This calibration can be achieved, for example, by the followingstructure. Namely, it is a structure wherein a pressure calculationmeans, into which outputs of the above-described pressure sensors areinputted, is provided, and in the pressure calculation means, based onthe above-described difference in characteristics determined, outputcharacteristics of one pressure sensor is calibrated on the basis ofoutput characteristics of the other pressure sensor. By this, the outputcharacteristics of both pressure sensors can be made even in software,and even if the differential pressure is small, it can be accuratelydetermined. Namely, in a condition where refrigerant flows, using theabove-described calibrated output characteristics of the pressuresensor, a differential pressure between the upstream and downstreamsides of the orifice may be calculated from outputs of both pressuresensors.

Further, if a relationship between a flow rate of refrigerant and adifferential pressure between the upstream and downstream sides of theorifice is being determined by an examination and the like in advance,from the above-described calculated differential pressure, a flow rateof refrigerant at that time can be accurately calculated referring tothe predetermined relationship between a flow rate of refrigerant and adifferential pressure between the upstream and downstream sides of theorifice.

Further, if a relationship between a flow rate of refrigerant and atorque of the compressor in the refrigeration cycle is being determinedby an examination and the like in advance, from the above-describedcalculated differential pressure, a torque of the compressor at thattime can be accurately calculated referring to the predeterminedrelationship between a flow rate of refrigerant and a torque of thecompressor in the refrigeration cycle.

Thus, if the compressor torque can be estimated accurately, by sending asignal of the above-described calculated torque of the compressor to acontrol unit for a drive source of the compressor, an optimum control ofthe drive source can be realized. In case where the drive source of thecompressor is a prime mover for a vehicle (an engine), by estimating thecompressor torque accurately and at real time, it can be reflected, forexample, to a fuel injection control of the engine, thereby contributingto save the fuel consumption of the vehicle, etc.

With respect to the above-described calibration of the outputcharacteristics of the pressure sensor, for example as described later,it can be carried out using a preset calculation equation having acorrection term. Alternatively, the above-described calibration of theoutput characteristics of the pressure sensor can also be carried outusing a map preset with a plurality of output characteristics.

The above-described difference in characteristics between outputcharacteristics of the pressure sensors is preferably determined after apredetermined time passes since the refrigeration cycle is stopped. Whena predetermined time passes since the refrigeration cycle is stopped,because the flow of refrigerant is in a stable condition, the differencein output characteristics can be determined more accurately.

Such a refrigeration cycle according to the present invention issuitable particularly for use in an air conditioning system for vehicleswhich requires an accurate information of compressor driving torque fromthe viewpoint of drive control of a prime mover for a vehicle, etc.Further, also from the viewpoint that the determination of thedifference between output characteristics of the pressure sensors andthe calibration between the pressure sensors can carried out in softwareand therefore can be inexpensively without requiring a space, it issuitable for use in an air conditioning system for vehicles whichstrongly requires space saving and cost down.

Effect According to the Invention

In the refrigeration cycle according to the present invention, when theorifice is disposed within the refrigeration circuit and thedifferential pressure between the upstream and downstream sides thereofis detected using two pressure sensors, the difference between outputcharacteristics of the respective pressure sensors can be adequately andeasily treated and absorbed in software, and an actual differentialpressure can be determined properly and accurately. Therefore, based onthe differential pressure determined accurately, the flow rate ofrefrigerant can be estimated accurately, and ultimately, it becomespossible to estimate the compressor torque accurately. Consequently, byapplying the refrigeration cycle according to the present invention,while achieving a high-accuracy control, and space saving and cost downas the whole of the refrigeration cycle, an air conditioning system forvehicles having an optimum formation can be realized.

BRIEF EXPLANATION OF THE DRAWINGS

[FIG. 1] FIG. 1 is a schematic diagram of a refrigeration cycleaccording to an embodiment of the present invention.

[FIG. 2] FIG. 2 is an enlarged sectional view showing an example of apart of an orifice and pressure sensors in the refrigeration cycledepicted in FIG. 1.

[FIG. 3] FIG. 3 is a diagram in characteristics showing an example ofcorrection of shift of output characteristics of one pressure sensorrelative to output characteristics of the other pressure sensor in therefrigeration cycle depicted in FIG. 1.

[FIG. 4] FIG. 4 depicts diagrams in characteristics showing examples ofP-h diagrams of the refrigeration cycle depicted in FIG. 1.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, desirable embodiments of the present invention will beexplained referring to figures.

FIG. 1 shows a schematic structure of a refrigeration cycle according toan embodiment of the present invention. In the figure, symbol 1indicates the whole of a refrigeration cycle, and refrigeration cycle 1has a compressor 2 for compressing refrigerant, a condenser 3 forcondensing the compressed refrigerant, an expansion valve 4 as apressure reduction-expansion mechanism for pressure reducing andexpanding the refrigerant sent from the condenser 3, and an evaporator 5for evaporating the refrigerant sent from the expansion valve 4. In thisembodiment, an orifice 7 for throttling the flow of refrigerant isprovided on a refrigerant path 6 between condenser 3 and expansion valve4 in the refrigerant circuit of refrigeration cycle 1, and at theupstream and downstream positions of the orifice 7 in the direction ofthe refrigerant flow, a first pressure sensor 8 and a second pressuresensor 9 each detecting the pressure of refrigerant are provided,respectively. Orifice 7 and first and second pressure sensors 8, 9provided in this refrigerant path 6 are disposed, for example, as shownin FIG. 2. These may be formed as an integrated unit.

The outputs of the detected pressures from the above-described firstpressure sensor 8 and second pressure sensor 9 are sent to pressurecalculation means 10. Although each pressure sensor 8 or 9 has outputcharacteristics representing a relationship between a detected pressure(P) and a sensor output (V) such as one shown in FIG. 3 for example,output V1 of first pressure sensor 8 and output V2 of second pressuresensor 9 relative to a detected pressure (P) may be slightly shiftedfrom each other originating from errors in manufacture of the respectivepressure sensors 8, 9, etc. As aforementioned, there is a case wheresuch a slight shift becomes a relatively large amount of shit in casewhere a differential pressure between the pressures detected by bothsensors. In pressure calculation means 10, with regard to outputcharacteristics representing a relationship between a detected pressureand a sensor output of each of pressure sensors 8, 9, a difference incharacteristics between output characteristics of both sensors isdetermined from outputs of both pressure sensors at a condition wherethe flow of refrigerant is stopped, preferably, from outputs of bothpressure sensors after a predetermined time (a time necessary forstabilizing the flow of the refrigerant at its condition being stopped)passes since refrigeration cycle 1 is stopped. Then, a correctioncalculation is performed so that, based on the determined difference incharacteristics, output characteristics of one pressure sensor iscalibrated on the basis of output characteristics of the other pressuresensor. In the example shown in FIG. 3, the calibration is performed insoftware so as to adjust the characteristics of output V2 of secondpressure sensor 9 to the characteristics of output V1 of first pressuresensor 8, for example, with regard to a reference pressure Pa. Sincethis calibration is performed under a condition where the outputs ofboth pressure sensors 8, 9 at the condition of the flow of refrigerantbeing stopped, that is, the pressures to be detected by both pressuresensors 8, 9 are basically in a same pressure (uniform pressure) basedon the outputs of both pressure sensors 8, 9, the calibration ispreformed accurately. By this, the output characteristics of bothpressure sensors 8, 9 can be made even in software (for example, basepoints such as zero points can be made even in software), and viapressure detection using the output characteristics made even, even incase where the differential pressure is small in an actual pressuredetection at a condition where the refrigerant flows, the differentialpressure can be accurately and properly determined.

Such a calibration of the output characteristics of pressure sensor 9can be carried out, for example, by using the following presetcalculation equation having a correction term (H) which corresponds tothe above-described difference between output characteristics.

Pa=A×V1+B=A×V2+B+H

Where, B is a constant.

Alternatively, although it is not depicted, the above-describedcalibration of the output characteristics of pressure sensor 9 can alsobe carried out by using a map preset with a plurality of outputcharacteristics.

If the differential pressure between the upstream and downstreampositions of orifice 7 is thus calculated accurately, by a conditionwhere a relationship between a flow rate of refrigerant and adifferential pressure between the upstream and downstream sides of theorifice is being determined by an examination and the like in advanceand the relationship is stored in memory, from the differential pressurecalculated as described above, by a refrigerant flow rate estimationmeans 11, a flow rate of refrigerant at that time can be accuratelycalculated referring to this predetermined relationship between a flowrate of refrigerant and a differential pressure between the upstream anddownstream sides of the orifice.

Furthermore, by a condition where a relationship between a flow rate ofrefrigerant and a torque of compressor 2 in refrigeration cycle 1 isbeing determined by an examination and the like in advance and therelationship is stored in memory, from the flow rate of refrigerantcalculated as described above, by a compressor torque estimation means12, a torque of the compressor 2 at that time can be accuratelycalculated referring to this predetermined relationship between a flowrate of refrigerant and a torque of the compressor 2 in therefrigeration cycle 1.

Then, if the compressor torque can be thus estimated accurately, asaforementioned, by sending a signal of the estimated compressor torqueto a control unit for a drive source of the compressor (for example, anengine for a vehicle), an optimum control of the drive source can berealized. In particular, in case where the drive source of thecompressor is a prime mover for a vehicle (an engine), by estimating thecompressor torque accurately and at real time, it can be reflected, forexample, to a fuel injection control of the engine, thereby contributingto save the fuel consumption of the vehicle, etc.

Where, with respect to the position provided with the above-describedorifice and the property for giving a pressure loss to the providedorifice, it is possible to optimize them from the viewpoint of theoperation property of refrigeration cycle 1. The operation property ofrefrigeration cycle 1 can be represented by a P-h diagram, for example,as shown in FIGS. 4 (A) and (B). Namely, by orifice 7 provided onrefrigerant path 6, a differential pressure between the upstream anddownstream sides of the orifice can be forcibly given, and it becomespossible to detect a differential pressure necessary, for example, forestimating the flow rate of refrigerant by first and second pressuresensors 8, 9. Then, it becomes possible to estimate the flow rate ofrefrigerant having a high correlation with this differential pressure byrefrigerant flow rate estimation means 11, and ultimately, to estimatethe compressor torque by compressor torque estimation means 12. At thattime, the stable and accurate detection of the differential pressurebetween the upstream and downstream sides of the orifice may contributeto an accurate estimation of refrigerant flow rate and an accurateestimation of compressor torque. In order to detect the differentialpressure between the upstream and downstream sides of the orificeaccurately at a stable condition, it is preferred to detect it at acondition where there is no phase change of refrigerant or an extremelysmall phase change. For example, as shown in FIG. 4(A), it is preferredto be set so that a differential pressure ΔP due to the orifice occursin the same liquid phase. However, for example, as shown in FIG. 4(B),even if a differential pressure ΔP occurs over the phase changingregion, although the accuracy may be reduced slightly, it is possible toestimate the refrigerant flow rate and the compressor torque at asufficiently high accuracy.

INDUSTRIAL APPLICATIONS OF THE INVENTION

The refrigeration cycle according to the present invention can beapplied to any refrigeration cycle requiring to determine thedifferential pressure between upstream and downstream sides of anorifice using the orifice and pressure sensors disposed at upstream anddownstream sides thereof, and from the point in that the calibration ofthe pressure sensor can be carried out in software inexpensively, inparticular, it is suitable for use in an air conditioning system forvehicles which strongly requires cost down.

EXPLANATION OF SYMBOLS

1: refrigeration cycle

2: compressor

3: condenser

4: expansion vale as pressure reduction-expansion mechanism

5: evaporator

6: refrigerant path

7: orifice

8: first pressure sensor

9: second pressure sensor

10: pressure calculation means

11: refrigerant flow rate estimation means

12: compressor torque estimation means

1. A refrigeration cycle wherein an orifice is provided within arefrigerant circuit, and pressure sensors are respectively provided onan upstream side and a downstream side of said orifice, characterized inthat, with regard to output characteristics representing a relationshipbetween a detected pressure and a sensor output of each of said pressuresensors, a difference in characteristics between output characteristicsof one pressure sensor and output characteristics of the other pressuresensor is determined based on outputs of both pressure sensors at acondition where a flow of refrigerant is stopped.
 2. The refrigerationcycle according to claim 1, wherein a pressure calculation means, intowhich outputs of said pressure sensors are inputted, is provided, and insaid pressure calculation means, based on said difference incharacteristics determined, output characteristics of one pressuresensor is calibrated on the basis of output characteristics of the otherpressure sensor.
 3. The refrigeration cycle according to claim 2,wherein, in a condition where refrigerant flows, using said outputcharacteristics of said pressure sensor calibrated, a differentialpressure between said upstream and downstream sides of said orifice iscalculated from outputs of both pressure sensors.
 4. The refrigerationcycle according to claim 3, wherein, from said differential pressurecalculated, a flow rate of refrigerant at that time is calculatedreferring to a predetermined relationship between a flow rate ofrefrigerant and a differential pressure between said upstream anddownstream sides of said orifice.
 5. The refrigeration cycle accordingto claim 4, wherein, from said flow rate of refrigerant calculated, atorque of a compressor at that time is calculated referring to apredetermined relationship between a flow rate of refrigerant and atorque of said compressor in said refrigeration cycle.
 6. Therefrigeration cycle according to claim 5, wherein a signal of saidtorque of said compressor calculated is sent to a control unit for adrive source of said compressor.
 7. The refrigeration cycle according toclaim 2, wherein calibration of said output characteristics of saidpressure sensor is carried out using a preset calculation equationhaving a correction term.
 8. The refrigeration cycle according to claim2, wherein calibration of said output characteristics of said pressuresensor is carried out using a map preset with a plurality of outputcharacteristics.
 9. The refrigeration cycle according to claim 1,wherein said difference in characteristics between outputcharacteristics of said pressure sensors is determined after apredetermined time passes since said refrigeration cycle is stopped. 10.The refrigeration cycle according to claim 1, wherein said refrigerationcycle is used for an air conditioning system for vehicles.